Cardiac myocyte differentiation: the Nkx2.5 and Cripto target genes in P19 clone 6 cells

NKX2-5 regulates human cardiomyogenesis via a HEY2 dependent transcriptional network

Congenital heart defects can be caused by mutations in genes that guide cardiac lineage formation. Here, we show deletion of NKX2-5, a critical component of the cardiac gene regulatory network, in human embryonic stem cells (hESCs), results in impaired cardiomyogenesis, failure to activate VCAM1 and to downregulate the progenitor marker PDGFRα. Furthermore, NKX2-5 null cardiomyocytes have abnormal physiology, with asynchronous contractions and altered action potentials. Molecular profiling and genetic rescue experiments demonstrate that the bHLH protein HEY2 is a key mediator of NKX2-5 function during human cardiomyogenesis. These findings identify HEY2 as a novel component of the NKX2-5 cardiac transcriptional network, providing tangible evidence that hESC models can decipher the complex pathways that regulate early stage human heart development. These data provide a human context for the evaluation of pathogenic mutations in congenital heart disease.

A gene regulatory network, including the transcription factor Nkx2-5, regulates cardiac development. Here, the authors show that on deletion of NKX2-5 from human embryonic stem cells, there is impaired cardiomyogenesis and changes in action potentials, and that this is regulated via HEY2.

Silencing of TBX20 gene expression in rat myocardial and human embryonic kidney cells leads to cell cycle arrest in G2 phase

Congenital heart diseases (CHDs) are the most common birth defects due to abnormal cardiac development. The T-box 20 (TBX20) gene is a member of the T-box family of transcription factors and encodes TBX20, which is essential for early heart development. In the present study, reduced TBX20 expression was observed in CHD tissue samples compared with normal tissues, and the function of TBX20 in Rattus norvegicus myocardial cells [H9c2(2-1)] and human embryonic kidney cells (HEK293) was investigated. TBX20 was silenced in H9c2 and HEK293 cells via transfection of small interfering RNA and short hairpin RNA duplexes, respectively, and TBX20 mRNA and protein levels were subsequently examined using reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and western blot analysis. Cell proliferation was assessed using a cell counting kit and proliferating cell nuclear antigen expression was determined by western blotting. Analysis of cell apoptosis was achieved by annexin V-fluorescein isothiocyanate/propidium iodide staining and a fluorometric terminal deoxynucleotidyl transferase dUTP nick-end labeling system. Cell cycle analysis was achieved using fluorescence-activated cell sorting, and, an RT-qPCR array was used to profile the expression of TBX20-related genes. Silencing of TBX20 in H9c2 and HEK293 cells significantly inhibited cell proliferation, induced cell apoptosis and led to G2/M cell cycle arrest. A reduction in cyclin B1 mRNA levels and an increase in cyclin-dependent kinase inhibitor 1B mRNA levels was observed, which indicated that cells were arrested in G2 phase. Concurrently, the mRNA levels of GATA binding protein 4 were increased in both cell lines, which may provide an explanation for the abnormal cardiac hypertrophy observed in patients with congenital heart disease. These results suggest that TBX20 is required for heart morphogenesis, and inhibition of TBX20 expression may lead to the suppression of cell proliferation and cell cycle arrest.

Nkx2-5 Regulates Tdgf1 (Cripto) Early During Cardiac Development

Congenital Heart Disease (CHD) is the most frequent and deadly birth defect. Patients with CHD that survive the neonatal period often progress to develop advanced heart failure requiring specialized treatment including cardiac transplantation. A full understanding of the transcriptional networks that direct cardiac progenitors during heart development will enhance our understanding of both normal cardiac function and pathological states. These findings will also have important applications for emerging therapies and the treatment of congenital heart disease. Furthermore, a number of shared transcriptional pathways or networks have been proposed to regulate the development and regeneration of tissues such as the heart. We have utilized transgenic technology to isolate and characterize cardiac progenitor cells from the developing mouse heart and have begun to define specific transcriptional networks of cardiovascular development. Initial studies identified Tdgf1 as a potential target of Nkx2-5. To mechanistically dissect the regulation of this molecular program, we utilized an array of molecular biological techniques to confirm that Nkx2-5 is an upstream regulator of the Tdgf1 gene in early cardiac development. These studies further define Nkx2-5 mediated transcriptional networks and enhance our understanding of cardiac morphogenesis.

Role of Cripto-1 during epithelial-to-mesenchymal transition in development and cancer

Epithelial-to-mesenchymal transition (EMT) is a critical multistep process that converts epithelial cells to more motile and invasive mesenchymal cells, contributing to body patterning and morphogenesis during embryonic development. In addition, both epithelial plasticity and increased motility and invasiveness are essential for the branching morphogenesis that occurs during development of the mammary gland and during tumor formation, allowing cancer cells to escape from the primary tumor. Cripto-1, a member of the epidermal growth factor-Cripto-1/FRL-1/Cryptic (EGF/CFC) gene family, together with the transforming growth factor (TGF)-β family ligand Nodal, regulates both cell movement and EMT during embryonic development. During postnatal development, Cripto-1 regulates the branching morphogenesis of the mouse mammary gland and enhances both the invasive and migratory properties of mammary epithelial cells in vitro. Furthermore, transgenic mouse models have shown that Cripto-1 promotes the formation of mammary tumors that display properties of EMT, including the down-regulation of the cell surface adherens junctional protein E-cadherin and the up-regulation of mesenchymal markers, such as vimentin, N-cadherin, and Snail. Interestingly, Cripto-1 is enriched in a subpopulation of embryonal, melanoma, prostate, and pancreatic cancer cells that possess stem-like characteristics. Therefore, Cripto-1 may play a role during developmental EMT, and it may also be involved in the reprogramming of differentiated tumor cells into cancer stem cells through the induction of an EMT program.

Stat3 directly controls the expression of Tbx5, Nkx2.5, and GATA4 and is essential for cardiomyocyte differentiation of P19CL6 cells

The transcription factor Stat3 (signal transducer and activator of transcription 3) mediates many physiological processes, including embryogenesis, stem cell self-renewal, and postnatal survival. In response to gp130 receptor activation, Stat3 becomes phosphorylated by the receptor-associated Janus kinase, forms dimers, and enters the nucleus where it binds to Stat3 target genes and regulates their expression. In this report, we demonstrate that Stat3 binds directly to the promoters and regulates the expression of three genes that are essential for cardiac differentiation: Tbx5, Nkx2.5, and GATA4. We further demonstrate that Tbx5, Nkx2.5, and GATA4 expression is dependent on Stat3 in response to ligand treatment and during ligand-independent differentiation of P19CL6 cells into cardiomyocytes. Finally, we show that Stat3 is necessary for the differentiation of P19CL6 cells into beating cardiomyocytes. All together, these results demonstrate that Stat3 is required for the differentiation of cardiomyocytes through direct transcriptional regulation of Tbx5, Nkx2.5, and GATA4.

Skeletal and cardiac myogenesis accompany adipogenesis in P19 embryonal stem cells

P19 embryonic carcinoma cells resemble normal embryonic stem (ES) cells. They generate cardiac and skeletal myocytes in response to retinoic acid (RA) or oxytocin (OT). RA treatment followed by exposure to triiodothyronine (T3) and insulin induces ES cells differentiation into adipocytes and skeletomyocytes. On the other hand, OT (10(-7) M) was reported to inhibit 3T3 preadipocyte maturation. The present work was undertaken to determine whether P19 cells have an adipogenic potential that could be affected by OT. Cells were treated with RA (10(-6) M)/T3+insulin (adipogenic protocol) or 10(-7) M OT (cardiomyogenic protocol), and analyzed by polymerase chain reaction, immunotechniques, and cytochemistry. Oil-Red-O staining and expression of peroxisome proliferator-activated receptor-gamma (PPARgamma) and aP2 indicated the generation of adipocytes in cultures submitted to the adipogenic protocol. Contracting cells were also generated. Cells positive for sarcomeric actinin and negative for cardiac troponin inhibitor (cTpnI) indicated generation of skeletomyocytes, and cTpnI positive cells revealed generation of cardiomyocytes. Levels of cTpnI and of the skeletal marker MyoD were almost similar in both protocols, whereas no Oil-Red-O staining was associated with the cardiomyogenic protocol. Addition of 10(-7) M OT to the adipogenic protocol did not affect Oil-Red-O staining and PPARgamma expression. Interestingly, Oct3/4 pluripotency marker disappeared in the adipogenic protocol but remained expressed in the cardiomyogenic one. P19 cells thus have an adipogenic potential non affected by 10(-7) M OT. RA/T3+insulin combination generates a larger spectrum of mesodermal cell derivatives and is a more potent morphogenic treatment than OT. P19 cells could help investigating mechanisms of cell fate decision during development.

Induction of Id2 expression by cardiac transcription factors GATA4 and Nkx2.5

Inhibitor of differentiation/DNA binding (Id) proteins function as a regulator of helix-loop-helix proteins participating in cell lineage commitment and differentiation. Here, we observed a marked induction of Id2 during cardiomyocyte differentiation from P19CL6 murine embryonic teratocarcinoma stem cells, prompting us to investigate the upstream regulatory mechanism of Id2 induction. Computer analysis of Id2 promoter and subsequent electrophoretic mobility shift assay revealed several binding sites for GATA4 and Nkx2.5 within the Id2 promoter. By further deletion and mutation analysis of the respective binding site, we identified that two motifs located at -497/-502 and -264/-270 were functionally important for Id2 promoter activation by GATA4 and Nkx2.5, respectively. Overexpression of GATA4 and/or Nkx2.5 induced not only Id2 promoter activity but also Id2 protein expression. Additionally, Id proteins significantly inhibit the GATA4 and Nkx2.5-dependent transcription, suggesting Id proteins may play a regulatory role in cardiogenesis. Collectively, our results demonstrate that GATA4 and Nkx2.5 could be one of the upstream regulators of Id2.

MEF2C is activated by multiple mechanisms in a subset of T-acute lymphoblastic leukemia cell lines

In T-cell acute lymphoblastic leukemia (T-ALL) the cardiac homeobox gene NKX2-5 (at 5q35) is variously deregulated by regulatory elements coordinating with BCL11B (at 14q32.2), or the T-cell receptor gene TRD (at 14q11.2), respectively. NKX2-5 is normally expressed in developing spleen and heart, regulating fundamental processes, including differentiation and survival. In this study we investigated whether NKX2-5 expression in T-ALL cell lines reactivates these embryonal pathways contributing to leukemogenesis. Among 18 known targets analyzed, we identified three genes regulated by NKX2-5 in T-ALL cells, including myocyte enhancer factor 2C (MEF2C). Knockdown and overexpression assays confirmed MEF2C activation by NKX2-5 at both the RNA and protein levels. Direct interactions between NKX2-5 and GATA3 as indicated by co-immunoprecipitation data may contribute to MEF2C regulation. In T-ALL cell lines LOUCY and RPMI-8402 MEF2C expression was correlated with a 5q14 deletion, encompassing noncoding proximal gene regions. Fusion constructs with green fluorescent protein permitted subcellular detection of MEF2C protein in nuclear speckles interpretable as repression complexes. MEF2C consistently inhibits expression of NR4A1/NUR77, which regulates apoptosis via BCL2 transformation. Taken together, our data identify distinct mechanisms underlying ectopic MEF2C expression in T-ALL, either as a downstream target of NKX2-5, or via chromosomal aberrations deleting proximal gene regions.

A multiple retinoic acid antagonist induces conotruncal anomalies, including transposition of the great arteries, in mice

BACKGROUND

The morphogenetic mechanisms that are responsible for the transposition of the great arteries are still largely unknown, mainly because this malformation is very difficult to experimentally reproduce. The aim of the present study was to test the effect of BMS-189453, a retinoic acid antagonist, on murine heart morphogenesis.

METHODS

We administered this drug at 5 mg/kg body weight (twice, at a 12-h interval) to pregnant mice on 6.25/6.75 days postcoitum (dpc) (Group A), 6.75/7.25 dpc (Group B), 7.25/7.75 dpc (Group C), 7.75/8.25 dpc (Group D), or 8.25/8.75 dpc (Group E). At birth, the anatomical features of fetuses were evaluated by stereomicroscopic examination.

RESULTS

In Group A (18 fetuses), cardiovascular anatomy was normal in 10 (56%) cases, and 8 (44%) fetuses presented with transposition of the great arteries. In Group B, no fetuses were obtained. In Group C (78 fetuses), cardiovascular anatomy was normal in 19 (24%) cases, while 59 (76%) mice presented with various types of cardiac defects, including 48 transpositions of the great arteries (61%). In Group D (80 fetuses), cardiac defects were seen in 22 (27%) mice: 14 of these (17%) were transpositions of the great arteries. In Group E (72 fetuses), cardiovascular anatomy was normal in all cases. Of 248 fetuses analyzed, 87% presented with thymic aplasia or hypoplasia, and 20% presented with meroanencephalia and/or rachischisis.

CONCLUSIONS

Transposition of the great arteries can be consistently reproduced in mice by administration of a retinoic acid competitive antagonist on 7.5 dpc.

Nitric oxide signaling in oxytocin-mediated cardiomyogenesis

Oxytocin (OT), a hormone recently identified in the heart, induces embryonic and cardiac somatic stem cells to differentiate into cardiomyocytes (CM), possibly through nitric oxide (NO). We verified this hypothesis using P19 cells and P19 Clone 6 derivatives expressing a green fluorescent protein (GFP) reporter linked to cardiac myosin light chain-2v promoter. OT treatment of these cells induced beating cell colonies that were fully inhibited by N,G-nitro-L-arginine-methyl-ester (L-NAME), an inhibitor of NO synthases (NOS), partially reduced by 1400W, an inhibitor of inducible NOS, and ODQ, an inhibitor of NO-sensitive guanylyl cyclases. The NO generator S-nitroso-N-acetylpenicillamine (SNAP) reversed the L-NAME inhibition of cell beating and GFP expression. In OT-induced cells, L-NAME significantly decreased transcripts of the cardiac markers Nkx2.5, MEF2c, alpha-myosin heavy chain, and less, GATA4, endothelial NOS, and atrial natriuretic peptide, as well as the skeletal myocyte (SM) marker myogenin. Image analysis of OT-induced P19Cl6-GFP cells revealed ventricular CM coexpressing sarcomeric alpha-actinin and GFP, with some cells exclusively expressing alpha-actinin, most likely of the SM phenotype. The OT-mediated production of CM, but not SM, was diminished by L-NAME. In P19 cells, exogenously added OT stimulated the expression of its own transcript, which was reduced in the presence of L-NAME. Surprisingly, L-NAME alone decreased the expression of anti-stage specific embryonic antigen-1 marker of the undifferentiated state and induced some beating colonies as well as GFP in P19Cl6-GFP cells. Collectively, our data suggest that the pleiotropic action of NO is involved in the initiation of CM differentiation of P19 cells and maintenance of their undifferentiated state.

Embryonic and adult stem cell-derived cardiomyocytes: lessons from in vitro models

For years, research has focused on how to treat heart failure by sustaining the overloaded remaining cardiomyocytes. Recently, the concept of cell replacement therapy as a treatment of heart diseases has opened a new area of investigation. In vitro-generated cardiomyocytes could be injected into the heart to rescue the function of a damaged myocardium. Embryonic and/or adult stem cells could provide cardiac cells for this purpose. Knowledge of fundamental cardiac differentiation mechanisms unraveled by studies on animal models has been improved using in vitro models of cardiogenesis such as mouse embryonal carcinoma cells, mouse embryonic stem cells and, recently, human embryonic stem cells. On the other hand, studies suggesting the existence of cardiac stem cells and the potential of adult stem cells from bone marrow or skeletal muscle to differentiate toward unexpected phenotypes raise hope and questions about their potential use for cardiac cell therapy. In this review, we compare the specificities of embryonic vs adult stem cell populations regarding their cardiac differentiation potential, and we give an overview of what in vitro models have taught us about cardiogenesis.